Long-Term Evolution (LTE) is the next step in cellular Third-Generation (3G) systems, which represents basically an evolution of present mobile communications standards, such as Universal Mobile Telecommunication System (UMTS) and Global System for Mobile Communications (GSM). It is a Third Generation Partnership Project (3GPP) standard that provides throughputs up to 50 Mbps in uplink and up to 100 Mbps in downlink. It uses scalable bandwidth from 1.4 to 20 MHz in order to suit the needs of network operators that have different bandwidth allocations. LTE is also expected to improve spectral efficiency in networks, allowing carriers to provide more data and voice services over a given bandwidth. LTE-Advanced (LTE-A), an evolution of LTE, is being standardized in LTE Release 10 and beyond. It is aimed at fulfilling International Mobile Telecommunications (IMT)-Advanced requirements, whose capabilities go beyond those of IMT-2000 and include enhanced peak data rates to support advanced services and applications (100 Mbps for high mobility, and 1 Gbps for low mobility).
In LTE systems, there are five types of downlink reference signals defined as follows:                Cell-specific reference signal (CRS)        Multicast-Broadcast Single Frequency Network (MBSFN) reference signal        UE-specific reference signal (DM-RS)        Positioning reference signal (PRS)        CSI reference signal (CSI-RS)        
There is one reference signal transmitted per downlink antenna port.
Cell(-specific) Reference Signals (CRSs) are transmitted in all downlink subframes in a cell supporting Physical Downlink Shared Channel (PDSCH) transmission. Cell-specific reference signals are transmitted on one or several of antenna ports 0 to 3. To facilitate the estimation of the channel characteristics, LTE uses cell reference signals (pilot symbols) inserted in both time and frequency. These pilot symbols provide an estimate of the channel at given locations within a subframe. Through interpolation it is possible to estimate the channel across an arbitrary number of subframes. A cell-specific reference signal is transmitted in each physical antenna port and it is used for both demodulation and measurement purpose. Cell reference signals are used for cell search and initial acquisition, downlink channel estimation for coherent demodulation/detection at the UE, and downlink channel quality measurements.
One of the biggest issues generally perceived as critical for LTE deployments is inter-cell interference. Orthogonal Frequency-Division Multiple Access (OFDMA) does not provide any protection when users receive significant interference from adjacent cells operating at the same carrier frequency. Specific interference cancellation (IC) techniques are therefore being explored at both the network and the devices side. The latter case relies on the support of advanced IC techniques at the device, like so-called Successive Interference Cancellation (SIC) or Parallel Interference Cancellation (PIC), which are of fast-growing interest. Indeed some of the solutions proposed by 3GPP for interference coordination in LTE-A rely upon device support of SIC/PIC capabilities.
SIC techniques at devices require detailed knowledge of the physical parameters describing the observed interference, like the modulation and coding scheme (MCS), in order to be able to decode and cancel interference prior to obtaining the desired signals.
Control channels IC usually benefit from pre-defined MCS formats, therefore relieving the network from signalling the applicable MCS to the devices. However data channels employ dynamic MCS formats to the different users in a subframe basis, and devices cannot therefore assume any a priori MCS format thus complicating SIC operation.
Multiple-Input Multiple-Output (MIMO) receivers currently implement SIC techniques for efficient decoding of the different streams in spatial multiplexing, usually in the form of Minimum Mean-Squared Error (MMSE)-SIC receivers. However these techniques only address inter-stream interference between the spatial streams intended for a given user, but are not able to cope with interfering signals coming from other neighbour cells.
Therefore, there is a need in the state of the art for more efficient ways of assisting user devices in performing advanced inter-cell interference cancellation techniques.